Not Applicable.
Not Applicable.
1. Field of Invention
The present invention is directed generally to wireless communication networks and, more particularly, to methods for estimating signal strengths in the design of wireless communication networks.
2. Description of the Background
Wireless local area networks (WLANs) were originally intended to allow wireless connections to a wired local area network (LAN), such as where premises wiring systems were nonexistent or inadequate to support conventional wired LANs. A block diagram of a typical WLAN 10 is illustrated in FIG. 1. The WLAN 10 includes a mobile device 12 including a network adapter (NA) 14, a number of access points (APs) 161-n, and a wired LAN 18. The APs 16 may be radio base stations, each mounted in a separate fixed position and connected to the wired LAN 18. The NA 14 communicates with the APs 16 by formatted wireless communication signals to provide an interface between the computing device 12 and the wired LAN 18. Because network adapters 14 are now available in compact PC card form, WLANs are often used to service mobile computing devices, such as laptop computers and personal digital assistants (PDAs), thus providing mobile connectivity to data networks, such as the Internet or an intranet.
In designing a WLAN, care must be taken in locating the APs 16 to ensure adequate radio coverage throughout the service area of the WLAN 10, while minimizing the costs associated with the installation of each AP 16. The APs 16 must be configured to eliminate coverage gaps and to provide adequate coverage for areas of highly-concentrated wireless traffic. The APs 16, however, must not be placed so closely that proximate APs 16 interfere with each other. Implementing a WLAN 10 inside a building complicates the design because the layout and construction of the building affect the wireless signal transmissions between the NAs 14 and the APs 16. For example, while wood, plaster, and glass are not serious barriers to the WLAN radio transmissions, brick and concrete walls can attenuate the signals beyond an acceptable threshold. In addition, the greatest obstacle to the wireless transmissions between the NAs 14 and APs 16 commonly found in all building environments is metal. For example, the metal used in desks, filing cabinets, reinforced concrete, and elevator shafts can significantly attenuate the signals transmitted between the NAs 14 and the APs 16, thus degrading network performance.
In addition, the communication schemes for transmitting signals between the NAs 14 of the mobile devices 12 and the APs 16 are typically contention-oriented, such as those compliant with, for example, the IEEE 802.11 protocol, in order that all the mobile units in the environment may share the limited bandwidth resource. Such a contention-oriented protocol makes signal interference between the APs 16 undesirable because if one AP 16 can xe2x80x9chearxe2x80x9d another, it will defer to the other just as it would defer to a mobile device transmitting within its coverage area. Thus, signal interference between APs 16 degrades performance. Similarly, if a mobile device 12 can be heard by more than one AP 16, all the APs 16 in communication with the mobile device will defer.
Because radio propagation inside a building is frequently anomalous and seldom completely predictable, the design process for an indoor wireless installation is ordinarily iterative, including steps for (i) determination of an initial design, (ii) adjustment of the initial design, and (iii) final measurement and documentation. After the initial design is complete, the APs 16 may be temporarily installed at the locations specified in the initial design. The coverage areas of these points and the overlaps in the coverage area may be measured. Typically, coverage gaps and/or excessive overlaps are found. Based on the measured results, the AP locations may be adjusted as needed. Thereafter, more measurements may be taken and the installation reconfigured until an acceptable installation is found.
The step of adjusting the locations of the APs 16 in order to re-test the configuration of the installation is expensive and time consuming. It commonly requires reconfiguring the locations of the APs 16 and generating additional sets of signal strength measurements to determine whether coverage gaps and/or excessive overlaps exist. Accordingly, there exists a need for a manner in which to efficiently estimate AP coverage patterns in an indoor wireless installation.
According to one embodiment, the present invention is directed to a method for estimating signal strengths for a wireless environment. The method includes measuring a strength of a first radio signal at a plurality of locations in the environment, wherein the radio signal is transmitted from a radio transmitter at a first location, estimating the strength of the first radio signal at each of the plurality of locations, and estimating a strength of a second radio signal at the plurality of locations, wherein the second radio signal corresponds to a signal transmitted from one of the plurality of locations, based on a difference between the measured signal strength and the estimated signal strength for the first radio signal.
The present invention provides an advantage over prior art techniques for determining whether a particular configuration of radio transmitters for an environment, especially access points for a wireless indoor LAN, will be acceptable without having to physically move radio transmitters throughout the environment to generate signal strength measurements for each possible configuration. Accordingly, the present invention is more time efficient and less expensive than prior art techniques. These and other benefits of the present invention will be apparent from the detailed description hereinbelow.